It also helps not only to have IR or IMC training under VMC conditions, but to be actually in the clouds and experience that. It's a big difference to flying 'under the hood'
Agree! However, it's illegal. In order to penetrate the clouds, you have file an IFR flight plan. In order to do that your instructor needs to be an IR instructor and you have to be registered as an instrument student.
My instructor has done it to practice 180° turns and to get a feeling (very different thing doing this under the hood in VMC or in a turbulent cumulus cloud). I'm very thankful for the experience but he was breaking the rules. Stupid!